Data communications over cellular telephone networks can be carried out using various technologies such as packet data wireless connections and modem communication over a voice channel of the cellular network. For this latter means of data communication, the modulated data from the modems must pass through the cellular network equipment, including vocoders designed to compress speech data for more efficient transference. Newer generation vocoders such as those using the EVRC-B codec can interfere with the transmission of modem signaling tones that are otherwise used to establish the data communications between modems over the cellular voice channel.